A polyamide resin has superior workability (or processability), chemical resistance and heat resistance and a low gas permeability, and therefore, has been broadly used for injection molded products, extruded products, blown products, films, etc., utilizing these properties. However, since a polyamide resin is not necessarily sufficient in terms of impact resistance, fatigue resistance, etc., the improvement of these properties under a usage environment receiving dynamic strain has been required. As a means for improving the impact resistance of a polyamide resin, it is known in the art to blend a modifier composed of an elastomer ingredient (see, for example, U.S. Pat. No. 4,174,358 and U.S. Pat. No. 4,594,386. However, for the fatigue resistance, depending upon the usage environment, the mechanism of failure is complicated, a sufficient effect of improvement could not been obtained with just blending an elastomer. Various modifiers for polyamide resins, in particular nylons have been proposed by manufacturers. However, under extension and flexing fatigue environments, a large load acts on interface of the polyamide-modifier and inside the modifier whereby interfacial failure or modifier failure occur and a sufficient effect of improvement by the modifier cannot be obtained.